The invention relates generally to medical fluid flow valves and more particularly, to valves that automatically shut off when fluid reaches a certain level.
During hospitalization, a physician may desire to infuse a medical fluid into a patient""s bloodstream. The medical fluid may be for therapy, the replacement of body fluid, or for other purposes. During the administration of medical fluids to a patient, it is important that amounts of air exceeding a certain threshold not be infused. If too large a quantity of air is allowed to enter the patient""s blood stream, an embolism could result, which can be a serious condition.
In infusing medical fluids, many times a medical fluid reservoir, such as a bag or bottle, is hung in an inverted position and its contents are allowed to infuse into the patient either through gravity or with the aid of an infusion pump that accurately controls the flow rate in accordance with the physician""s instructions. A fluid administration set is used to conduct the fluid from the bag to the patient and comprises a fluid line that is connected to the inverted bag at one end, referred to as its proximal end, and is connected to a catheter inserted into the vein of a patient at the other end, referred to as its distal end. Many fluid infusion administration sets include a device known as a drip chamber. This device may include a sharpened spike for penetrating the stopper or septum of the inverted bag, bottle, or other type of container to gain access to the contents of that container. The spike conducts the contents of the container to a chamber that includes a precise drop former located at its inlet or upstream end. The drop former forms drops having a known quantity of liquid. The number of drops may be counted per unit of time to determine the flow rate of fluid into the patient. The drop former is located within a chamber in which the formed drops fall or xe2x80x9cdrip,xe2x80x9d and that chamber has an outlet, or downstream end, that connects to the tubing of the administration set. That tubing provides a conduit for the medical fluid to flow to the patient.
Nurses monitor the drip chamber for the presence of drops to be sure that the medical fluid reservoir has not emptied. As is well known to those skilled in the art, drip chambers are designed to continuously have a certain level of fluid within the chamber when the flow of fluid into the patient is proceeding normally, such as 3 ml. When the fluid in the reservoir and tube above the drip chamber is exhausted and drops cease to fall, the level of fluid in the drip chamber will decrease until eventually it is empty. Unless the administration set tubing is clamped or other action is taken, air may then enter the administration tubing to which the drip chamber is connected. Thus, an empty fluid reservoir may result in air being drawn into the drip chamber and tubing and consequently being infused into the patient unless the line is clamped or other action is taken.
Additionally, if the fluid level in the drip chamber is permitted to decrease too far, the nurse cannot replace the fluid reservoir with another unless the entire administration set is primed again to remove air that has found its way into the line. Priming the line takes time and it is desirable to provide devices that control the entry of air into the fluid line so that the procedure of re-priming is not necessary. In particular, it is desirable that enough fluid remain in the drip chamber when the present reservoir is exhausted so that a new fluid reservoir may be connected to the drip chamber and the flow of new fluid to the patient begin without the need for re-priming the fluid administration set.
In another application, the drip chamber may form a part of a burette and be located at the distal, or downstream, end of the burette chamber. In such a case, the drip chamber would not include a sharpened spike but would include the other elements discussed above. In yet a further arrangement, the drip chamber may not have a spike but may instead be fed at its upstream end by a length of tubing that has an integral spike for establishing communication with the container of medical fluid. The spike on the tubing is inserted into the container and the fluid flows through the short length of tubing into the drip chamber.
Nurses are very busy and it is desirable to provide a device that automatically shuts off flow when the medical fluid container becomes depleted. Therefore, those in the development of medical fluid infusion devices have created various shut off valves that have been incorporated directly into the drip chamber device to automatically shut off fluid flow through the fluid line once the medical fluid reservoir has emptied. Some of these systems are relatively complex while some are simpler. One class of such devices uses a device that floats in the liquid of the drip chamber and has a valve seat located at the downstream end of the drip chamber. As is typical in these designs, the floating device floats at a certain level in the fluid dependent upon the buoyancy of the floating device. The floating device is designed to seat when the fluid in the chamber decreases to a certain low level. As the level decreases, the float approaches nearer and nearer the valve seat until it finally seats and shuts off flow thereby providing an automatic shut off valve that does not require constant monitoring by a nurse.
Problems have arisen with such devices, one of which is that the floating device may not properly seat and completely shut off flow. Under adverse conditions, such as where the administration set may be moving from side to side or oriented at an angle other than directly vertical, the valve device may be slow in seating and fluid shut off may be delayed, thus raising the possibility that air may enter the administration line.
A variation in this type of automatic shut off valves has incorporated magnetic force to assist in fluid line shut off. The force of magnetic attraction is used between a float located in the drip chamber and a stationary part, such as a valve seat, to shut off fluid flow in the administration line. Such an approach has an advantage in that it acts as a latching-type of valve. That is, the magnetic field or fields used have a field strength that increases non-linearly as the distance between the magnetic devices decreases. While some attraction exists when the magnetic devices are relatively far apart from each other, that attraction increases as they near each other until finally, the magnetic force provided by their attraction overcomes the buoyancy of the float in the drip chamber and it is drawn into a seating position in this magnetically activated valve thus positively shutting off fluid flow.
This magnetic force developed between the two parts tends to hold the valve in the shut off position better than other valves that rely only on gravity. Where prior floats relied only on their weight to seal the fluid line, the use of a magnetic force as well as the weight of the float results in a better chance that the float will completely seal and shut off flow. The use of a magnetic force also tends to draw the float into the seat when the drip chamber is tilted out of vertical alignment. Once seated, the valve is xe2x80x9clatchedxe2x80x9d in that some mechanical force beyond that provided by the mere buoyancy of the float developed by newly added fluid is required to separate the float from its valve seat. Even filling the drip chamber with fluid will typically not dislodge the float from the valve seat in these devices. The force of the magnetic attraction to the seat exceeds the force provided by the buoyancy of the float and some mechanical force is necessary to dislodge the two. Typically, the nurse will squeeze the wall of the drip chamber to dislodge the float from the valve seat so that it may rise to the level of the fluid.
However, problems have arisen in such devices. Magnetic devices comprising metallic elements should not be exposed to medical fluid in the infusion line. Additionally, some prior devices have uniquely shaped float devices that must be installed in a particular orientation in the drip chamber as the device is manufactured. Failure to properly orient the parts during manufacture can result in a valve that does not completely seal and may therefore need to be scrapped. Such requirements increase manufacturing costs. In other devices, the seal is formed between relatively rigid surfaces, and this configuration may give rise to the problem of leakage at the seal due to imperfections, or lack of fit, between the sealing surfaces. In yet another arrangement, the two devices comprising the valve, at least one of which is a magnet, may not be aligned so that the lines of magnetic flux between the two devices are then not optimally effective. In such a case, a larger magnet is used, which can increase costs.
Hence, a need has been recognized by those skilled in the art for an automatic shut off valve usable in fluid administration lines that is efficient and reliable in operation. A need has also been recognized for an improved automatic fluid shut off valve that uses magnetic force to assist in the shut off. Yet a further need has been recognized for a magnetic fluid shut off valve that is relatively easy to manufacture and has lower manufacturing costs. The present invention fulfills such needs and others.
Briefly and in general terms, the present invention is directed to an apparatus and method for a magnetic automatic shut off valve for use in regulating the flow of medical fluid. In a first aspect, an automatic shut off valve for use in regulating the flow of medical fluid comprises a container adapted to contain medical fluid, the container having an upstream end and a downstream end and defining an exit orifice at the downstream end, a hollow float defining an internal post, the float disposed within the container, a first attraction element disposed within the float and disposed over the post and adapted to slide along the post, and a second attraction element disposed at the exit orifice, the first and the second attraction elements being formed of materials that produce magnetic attraction between the two elements, wherein the materials that produce the magnetic attraction between the two elements are selected so that the strength of the magnetic attraction between the two elements is such that when the fluid in the container falls to a level near depletion, the first and second attraction elements are attracted to each other with sufficient force to move the float into a position that seals the downstream end against fluid flow.
In more detailed aspects, the automatic shut off valve further comprises a valve seat located proximate the exit orifice at the downstream end of the container, the valve seat having a first sealing surface, wherein the float includes a second sealing surface configured to mate with the first sealing surface and form the seal against fluid flow. A third sealing surface is disposed at a fixed position within the container at a selected location away from the first sealing surface, and a fourth sealing surface located on the float and configured to mate with the third sealing surface to provide a greater seal against fluid flow. The float has a section of increased diameter that forms the fourth sealing surface, wherein the section of increased diameter forming the third sealing surface is located substantially at the center of the float. Wherein the third sealing surface comprises a membrane of pliable material formed substantially in the shape of a ring and having a smaller inner diameter than an outer diameter of the fourth sealing surface of the float wherein the third sealing surface and the fourth sealing surface come into contact with each other thereby sealing against fluid flow when the float is disposed such that the first and second sealing surfaces are in contact.
In another aspect, the automatic shut off valve further comprises a first sealing surface disposed at a fixed position within the container proximate the exit orifice at the downstream end of the container, and a third sealing surface disposed at a fixed position within the container on a container wall at a selected location away from the first sealing surface, wherein the first and third sealing surfaces engage the float to form seals against fluid flow when the float is moved into the position that seals the downstream end against fluid flow due to the magnetic attraction between the two elements. The float includes opposite ends, each end of which includes a second sealing surface configured to mate with the first sealing surface, and the float includes a generally cylindrical section that provides a fourth sealing surface configured to mate with the third sealing surface, wherein the first and second sealing surfaces form a seal against flow and the third and fourth sealing surfaces form another seal against flow when the float has been moved into the position that seals the downstream end against fluid flow due to the magnetic attraction between the two elements.
In yet a further aspect, the float comprises two substantially identical halves joined together to form the float, each float half including a half of the post such that when the substantially identical float halves are joined together, the entire internal post is formed. The float is generally cylindrical with a larger diameter cylindrical section located at the longitudinal center of the float, the float includes opposing ends, and the first attraction element is disposed over the post such that it may freely slide along the post, whereby the float may be inserted into the container with either of the opposing ends facing the exit orifice at the downstream end of the container and the first attraction element will slide along the internal post towards the second attraction element to establish a magnetic interaction with the second attraction element.
In more detailed aspects, the first attraction element has an inner opening larger in diameter than the diameter of the post, and the outer diameter of the first attraction element has a size that is smaller than the inner diameter of the hollow float, whereby the first attraction element is free to slide along the post within the float.
In yet a further aspect, the float has a length that exceeds an inner diameter of the container.
In yet another more detailed aspect, at least one of the first and second attraction elements comprises a magnet with the strength of the magnetic force produced by the magnet selected so that the magnet will attract the float to the valve seat for shutting off flow when a selected level of fluid remains in the container. The strength of the magnetic force produced by the magnet is also selected so that the float will align itself with the valve seat when the container is disposed at an angle other than vertical.
In further aspects, the float has a longitudinal axis and is rotationally symmetrical about the longitudinal axis. The float is also symmetrical about a plane perpendicular to the float""s longitudinal axis, the plane being located through the center of the float.
In accordance with method aspects, a method of automatically shutting off the flow of medical fluid from a container having an upstream end and a downstream end and defining an exit orifice at the downstream end comprises disposing a first attraction element over a post disposed within a hollow float so that the first attraction element may slide freely along the post, disposing a second attraction element at the exit orifice, the first attraction element and the second attraction element being formed from materials that produce magnetic attraction between the two elements, and inserting the float into the container so that, when fluid in the container falls to a level near depletion, the first and second attraction elements are attracted to each other with sufficient force to move the float into a position that seals the downstream end to fluid flow.
In further method aspects, the method further comprises forming the float from two substantially identical halves joined together, each float half including a half of the post such that when the substantially identical float halves are joined together, the entire internal post is formed. The method also comprises forming the float to be generally cylindrical with a larger diameter cylindrical section located at the longitudinal center, and with the float having opposing ends, and disposing the first attraction element over the post such that the first attraction element may freely slide along the post, whereby the float may be inserted into the container with either of the opposing ends facing the exit orifice at the downstream end of the container and the first attraction element will slide along the internal post towards the second attraction element to establish a magnetic interaction with the second attraction element.
Additional aspects of the method of automatically shutting off the flow of medical fluid comprise forming the float to have a length that exceeds an inner diameter of the container, and forming the first and second attraction elements so that at least one comprises a magnet, and selecting the strength of the magnetic force produced by the magnet so that the magnet will attract the float to the valve seat for shutting off flow when a selected level of fluid remains in the container. Further, the method comprises selecting the strength of the magnetic force produced by the magnet to align the float with the valve seat when the container is disposed at an angle other than vertical.
Further detailed method aspects include forming the float such that it is rotationally symmetrical about a longitudinal axis, and forming the float such that it is symmetrical about a plane perpendicular to the float""s longitudinal axis, the plane being located through the center of the float.